physicscrap said:
ok so time just slows to an observer... How does a clock look slower from an observer? I still don't understand how "Launch a clock into space - any kind of clock that has sufficient accuracy - and then bring it back to Earth and it will not match a clock that has stayed on the ground." works. It is not clicking for me. Because you say there are no forces, just time. Well a clock that measures time via gears is somehow affected according to you, how is it affected in such a way that is slows down?
grrrahawrwafhawofghoaw;gou;wa! you I am confused
First let's deal with the mechanical clock vs. light clock issue. Remember that your mechanical clock itself is held together by electromagnetic forces. And these electomagnetic forces make themselves felt from atom to atom at the speed of light. So the forces holding the mechanical clock together form tiny little light clocks inside the mechanical clock itself.
The second issue is when you say:
I understand time as a universal measurement.
But time
isn't a universal measurement, it is a relative one. I know that this is a hard concept to grasp, because in everyday experience time sure seems to be a universal measurement.
You and a friend sychronize your watches, and he goes off on a train trip. You are sure that at any given moment you both will agree that your watches read the same time. When he returns, you compare watches and they still read the same. From this, and other experiences, you conclude that time is universal.
The problem is that at the speeds we normally deal with, the Relativity of time is just not apparent. Your watches
don't read the same time, it's just that the time difference is so small you'd never notice it.
An analogy is this:
Over small areas, the surface of the Earth seems flat. For centuries, people believed this to be true. As a result, "down" was considered a universal direction. Someone pointing down at one point of the Earth would be pointing in the same direction as anyone else at any other point. This is like universal time.
Of course the Earth's surface isn't flat, it is curved due to the Earth being a sphere. As a result, people standing on different points of the Earth point in different directions when they point "down" (if I was standind on a level surface in San Fransisco, and could see through the Earth to someone in London, they would seem to be "below" me and tilted at an angle. To them, I would be the one "below" and titled at an angle.) This is because we each have our own notion as how you measure "down".
This is like Relative time.
A universe with Relative time behaves differently than one with universal time. You can do experiments that can distinguish as to which type of universe we live in. All experiments to date agree with us living in a universe with Relative time.